The Early Development of Forest Fragmentation Effects on Birds

Abstract

The early development of forest fragmentation effects on forest organisms is poorly understood partly because most fragmentation studies have been done in agricultural or suburban landscapes, long after the onset of fragmentation. We develop a temporal model of forest fragmentation effects on densities of forest‐breeding birds and provide data from an active industrial forest landscape to test the model. The model and our empirical data indicate that densities of several forest‐dwelling bird species can increase within a forest stand soon after the onset of fragmentation as a result of displaced individuals packing into remaining habitat. Along with higher densities in the newly formed fragments, pairing success in one species, the Ovenbird (Seiurus aurocapillus), was lower in fragments than nonfragments, possibly due to behavioral dysfunction resulting from high densities. Thus, density was inversely related to productivity. The duration and extent of increased densities following onset of fragmentation depends on many factors, including the sensitivity of a species to edge and area effects, the duration and rate of habitat loss and fragmentation, and the proximity of a forest stand to the disturbance. Incipient forest fragmentation may affect populations differently from later stages of fragmentation when the geometry of the landscape has reached a more stable configuration. Our model and data indicate, for reasons unrelated to traditional edge effects, that large tracts of forest can be important because they are relatively free from the variety of plant and animal population dynamics that might take place near new edges, including the encroachment of individuals displaced by habitat loss.

Confounding factors in the detection of species responses to habitat fragmentation

“…In the short term, crowding effects (Bierregaard et al, 1992 ;Debinski & Holt, 2000) occur when organisms that survive the immediate process of habitat loss are concentrated into the much smaller amount of remaining habitat, thereby increasing population densities and species richness within habitat fragments (Collinge & Forman, 1998). For example, this displacement phenomenon (Hagan, Haegen & McKinley, 1996) occurred almost immediately following habitat loss in Amazonian bird communities (Lovejoy et al, 1986) and in grassland invertebrates of the western USA (Collinge & Forman, 1998), but was not observed at all for Lumholtz's tree kangaroo, Dendrolagus lumholtzi, following deforestation in tropical northern Australian (Newell, 1999). In the latter species, individuals exhibited strong site fidelity and chose to remain in the deforested, degraded habitat rather than move to nearby continuous forest (Newell, 1999).…”

An Estimate of Nest Loss in Canada Due to Industrial Forestry Operations

“…Schmiegelow et al 1997) has demonstrated that in the first year or two after winter-harvesting, migratory birds often pack into remaining forest stands resulting in an unnaturally high density. In some cases this has been shown to result in negative effects on the nesting success of birds in remnant stands because of increased resource competition (Hagan et al 1996). The same phenomena could occur in stands directly adjacent to summer harvested areas within the year of harvest but has not been tested to the best of our knowledge.…”

A monitoring program for Patagonian foxes based on power analysis

“…The operation of other processes could also be suspected. For example, a severe reduction of food in ranches could lead to crowding effects in the protected area, as has been suggested for other taxa after substantial habitat removal (Hagan et al 1996). Finally, similar monitoring approaches could be useful to manage the widespread predatorlivestock conflict, as long as predator populations occupy refuges or constitute conservation targets (Herfindal et al 2005;Fleming et al 2006).…”